Extreme Heat and Humidity = HUGE MPG gains

[SentraSE-R]

Temperature alone has a noticeable effect on fuel economy during the first few miles driven. It takes me about 4 miles to bring my fe up to 40 mpg in 45 degree weather, 2 miles to do it in 65 degree weather, and <1 mile to do it in 90 degree weather. Coastal California weather is consistently mild, and I can minimize the cold weather hit by avoiding short trips. my mileage logs show little if any seasonal/temperature effects on fe.

[Nerys]

Now you see I noticed the opposite. Temperature had (until now) VERY LITTLE effect on my fuel economy even from dead summer to dead of winter (pre ethanol). I do not typically make a lot of short trips just a lot of LONG trips so the effect of longer "warmup" is greatly spread out for me.

FUEL had an effect not temperature (a noticeable effect)

In the cold climes they "alter" the fuel and this alteration is horrible for fuel economy.

I noticed when I took winter blend gasoline and REMOVED the ethanol from it (and other stuff that came out in the process) My fuel economy not only jumped massively but jumped beyond even my normal "summer" highs.

its why I was so surprised to see such a large increase and more than that other people seeing the same increase.

Now I do notice that with the METRO temperature has a much larger "impact" than with my previous larger rides (van jeep etc..) In fact so much so (thankfully minimal effect on me) the metro flat out WILL NOT WARM UP AT ALL in dead of winter unless I drive it. Just idling it can not produce enough "HEAT" to warm itself faster than the atmosphere cools it down :-)

I think a lot of people MISSED the full force effect of this weather for a simple reason. Dilution. I use a LOT of gas. even in a metro. I filled up 4-5 times during that "hot spell"

The average person would not even get through a one tank during that spell so they won't see the same "impact" we see filling up so often. (long commute)

[mnmarcus]

Sentra SER,
What's the difference between hot FE and cold FE? (ie, is hot FE 2x more efficient?) Nery's father (-or bro?) saw 5 - 10% increase in FE. I'd assume most driving can't be that influenced by cold start up... unless you took a lot of short trips...

I'd guess air pressure would make a big difference, although nobody does a 1 hr pursuit bike race at extreme elevation. But, they don't do it at sea level either. Human powered may be vastly different than ICE powered.

[Nerys]

In the past. the difference between hot fe (summer) and cold fe (winter) was less than 1mpg ie background noise.

Once they introduced ETHANOL I saw "massive" swings in FE based on what actual % of ethanol was in that particular tank.

with the jeep my summer FE was 22-24 mpg my winter fe was 22-24 mpg with 24 being a little more "rare"

with the metro (not counting this summer) my summer fe was around 55-56mpg while my winter fe was around 47-48mpg averaged out.

the metro is my first truly "small" displacement car. even my jeep had a 4 liter I6 (best damned gas engine ever made IMHO)

I have a 74 thing but it does not get driven much and never in the winter and its rather old tech so not really comparable (30mpg was the average)

I also have an unusually even and long commute so the normal variations that nail people (cold startup in the winter) are diluted for me IE I don't see them much.

when you winter cold start a car for 5 miles on a 15 mile commute its 1/3 of your commute.

when you winter cold start a car for 5 miles no warm up at all start and go and then drive 54 miles. well its irrelevant.

[oil pan 4]

Originally Posted by Nerys

Hmmm what would cause pre ignition?

In 2007 compiled a list of known causes on my old laptop but dont have it with me.
From what I can remember some of the causes were:
Fuel octane grade too low
Ignition timing too far advanced
engine running too hot
spark plug heat range too hot
Improper air fuel ratio (too lean)
carbon build up in the combustion chamber
poor oil control allowing oil up into the combustion chamber
Excessive exhaust back pressure
Intake air too hot (under hood intake)
Or you are running a less than ideal compression ratio, operating temp and fuel octane setup.

That is about 1/3 of the original list. But most of the others were for high power applications.
Such as when the spark plug arm over heats, turning it into a little glow plug (normally a problem for people who run nitrous).

[SentraSE-R]

Originally Posted by mnmarcus

Sentra SER,
What's the difference between hot FE and cold FE? (ie, is hot FE 2x more efficient?) Nery's father (-or bro?) saw 5 - 10% increase in FE. I'd assume most driving can't be that influenced by cold start up... unless you took a lot of short trips...

If you're asking about hot ambient temp fe v. cold ambient fe, I estimate it's ~15-20% between 45 F and 85 F. I can pull 72 mpg on my 10 mile test loop in the Summer on a hot day. That drops to the mid-high 50s in the Winter. Before I was a hypermiler, I owned a 4WD SUV that got 11 mpg in the Summer (55 F) in AK, but 5 mpg in the Winter (32 F).

[t vago]

The standard "dry air" (0% humidity) composition at 59 F is about 21% oxygen. At 100 F and 95% humidity, approximately 7% of the atmosphere will be water vapor. Furthermore, the density change of the remaining oxygen, due to the temperature change from 59 F to 100 F, will further reduce the oxygen content by another 6% from dry air.

This means that air at 100 F and 95% humidity will contain approximately 87% of the oxygen present in air at 59 F and 0% humidity. In other words, your gasoline engine would have to run using air containing 18.3% oxygen, as opposed to 21%.

This decrease in O2 will force the driver to open up the throttle a little more to keep the same cruising speed. This will reduce pumping losses through the throttle plate and intake manifold, placing the engine nearer its ideal BSFC. The result is a measurable increase in fuel economy.

[larrybuck]

I am not a Mr. Science, and can't address the humidity issue, but I know that warmer fuel will be more efficent!

It would be nice if some of us regular people could figure out how to heat up the fuel to NEAR flashpoint with out blowing ourselves up!

Fuel lines running closer to, and heated by exhaust manifold/pipes would help, but every app. is different, how much patience, and test time can you muster?


You've probably heard about micro screening used in older carb applications to break up fuel droplets, and stretch the fuel further that way.

Has anyone tried a mesh approach w fuel injection??? Are the injectors too pre determined engineer wise to function when semi-crude differences are introduced to established SYSTEMS????

We always here about new performance chips available for modern vehs.

Does anyone on here have the capabilities to mpg custom chip ? It seems like there would be at least a small steady customer base at first, that would grow w worsening times in the future.

[oil pan 4]

Originally Posted by larrybuck

It would be nice if some of us regular people could figure out how to heat up the fuel to NEAR flashpoint with out blowing ourselves up!

You've probably heard about micro screening used in older carb applications to break up fuel droplets, and stretch the fuel further that way.

Has anyone tried a mesh approach w fuel injection??? Are the injectors too pre determined engineer wise to function when semi-crude differences are introduced to established SYSTEMS????

A few years ago I read about a guy that had an aftermarket fuel heater system installed in his all highway driven H3 and saw no result.

Back around 2006 I discovered little plastic turblance inducers found after the tips of injectors used on at least some GM fuel injected engines (made well before 2006), they may have sparyed through a plastic mesh, I do not fully recall. Injector tip accessories seem to have fallen out of favor in more recent years.

The best thing I found you can do to Gasoline to increase its combustion charistics is to increase its volitility (at least with a carb). I tested this between winter 2007 to summer 2008 by buying "winter fuel" and keeping it in a sealed metal barrel (not the standard 55 gallon, much smaller). I saved the fuel till summer time and used it to fill up 2 tanks, each tank picked up an unmistakable 2mpg and my engine seemed much happier running off high volitility gas in warm weather.
The oil companies/government adujsts volititaly by controling butane content.